feat: make crosswalk and stop-line offsets solvable

Step 1 of the control-marking task, and deliberately server-only: no handle is
drawn yet. This project already shipped a range handle for `profile.interval`,
which compileGeometry ignores, so the control dragged and changed nothing. The
consumer comes first now.

Two kinds join the taxonomy — `junction-crosswalk-inset` and
`junction-stop-line-offset`, both on the existing `junction-approach` anchor. The
solver writes them onto the approach entry, `applyDirectJunctionPlans` carries
them onto the compiled approach, and `compileControlMarkings` reads them in place
of the module constants it used for every junction. They move markings without
reshaping the junction, so unlike width and cutback they deliberately do not
trigger a boundary recompute.

`applyJunctionConstraint` becomes an explicit switch. Its trailing `else` had
meant every kind that was not approach-width fell through to the cutback
validator, so a new kind would have been silently validated and written as a
cutback. The same non-exhaustive shape in the test fixture's `valueFor` is fixed
the same way, and now throws for an unnamed kind rather than answering with a
corner radius.

design.md's taxonomy is updated with it — a test asserts the two cannot drift,
which is what caught the omission.

Measured on a 41-road workspace with 8 crossings: both constraints change their
marking geometry, neither drags the other, and out-of-range blocks instead of
clamping. That measurement is not in the suite: the synthetic junction resolves
`junction_inset_m` to 0 because its crossing never binds to a plan, and the
committed OSM fixture has no crossings at all. The tests assert the wiring the
handles will depend on — values reaching the approach entry, distinct branches,
blocking diagnostics — and the gap is recorded in the test itself.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.trellis/scripts/common/tasks.py

@@ -0,0 +1,112 @@
+"""
+Task data access layer.
+
+Single source of truth for loading and iterating task directories.
+Replaces scattered task.json parsing across 9+ files.
+
+Provides:
+    load_task          — Load a single task by directory path
+    iter_active_tasks  — Iterate all non-archived tasks (sorted)
+    get_all_statuses   — Get {dir_name: status} map for children progress
+"""
+
+from __future__ import annotations
+
+from collections.abc import Iterator
+from pathlib import Path
+
+from .io import read_json
+from .paths import FILE_TASK_JSON
+from .types import TaskInfo
+
+
+def load_task(task_dir: Path) -> TaskInfo | None:
+    """Load task from a directory containing task.json.
+
+    Args:
+        task_dir: Absolute path to the task directory.
+
+    Returns:
+        TaskInfo if task.json exists and is valid, None otherwise.
+    """
+    task_json = task_dir / FILE_TASK_JSON
+    if not task_json.is_file():
+        return None
+
+    data = read_json(task_json)
+    if not data:
+        return None
+
+    return TaskInfo(
+        dir_name=task_dir.name,
+        directory=task_dir,
+        title=data.get("title") or data.get("name") or "unknown",
+        status=data.get("status", "unknown"),
+        assignee=data.get("assignee", ""),
+        priority=data.get("priority", "P2"),
+        children=tuple(data.get("children", [])),
+        parent=data.get("parent"),
+        package=data.get("package"),
+        raw=data,
+    )
+
+
+def iter_active_tasks(tasks_dir: Path) -> Iterator[TaskInfo]:
+    """Iterate all active (non-archived) tasks, sorted by directory name.
+
+    Skips the "archive" directory and directories without valid task.json.
+
+    Args:
+        tasks_dir: Path to the tasks directory.
+
+    Yields:
+        TaskInfo for each valid task.
+    """
+    if not tasks_dir.is_dir():
+        return
+
+    for d in sorted(tasks_dir.iterdir()):
+        if not d.is_dir() or d.name == "archive":
+            continue
+        info = load_task(d)
+        if info is not None:
+            yield info
+
+
+def get_all_statuses(tasks_dir: Path) -> dict[str, str]:
+    """Get a {dir_name: status} mapping for all active tasks.
+
+    Useful for computing children progress without loading full TaskInfo.
+
+    Args:
+        tasks_dir: Path to the tasks directory.
+
+    Returns:
+        Dict mapping directory names to status strings.
+    """
+    return {t.dir_name: t.status for t in iter_active_tasks(tasks_dir)}
+
+
+def children_progress(
+    children: tuple[str, ...] | list[str],
+    all_statuses: dict[str, str],
+) -> str:
+    """Format children progress string like " [2/3 done]".
+
+    Args:
+        children: List of child directory names.
+        all_statuses: Status map from get_all_statuses().
+
+    Returns:
+        Formatted string, or "" if no children.
+    """
+    if not children:
+        return ""
+    # A child missing from active statuses has been archived (cmd_archive
+    # sets status=completed before moving the dir). Count it as done so
+    # parent progress doesn't regress when children are archived.
+    done = sum(
+        1 for c in children
+        if c not in all_statuses or all_statuses.get(c) in ("completed", "done")
+    )
+    return f" [{done}/{len(children)} done]"